The present invention relates to a method of manufacturing an electrically conductive contact layer and in particular a layer which adheres in an airtight manner both to the surface of a carrier of insulating material, such as glass, quartz or ceramics, and also to electrically conductive coatings on the insulating carrier. Gas discharge display devices for indicating numbers and symbols are known in flat constructions. They comprise two surface carriers made from insulating material which lie opposite one another at a small spacing, of which at least one carrier comprises glass. On the inner surfaces of these substrates facing one another are arranged electrodes which comprise electrically conductive coatings, particularly coatings made of tin oxide. Tin oxide (stannous or stannic oxide) coatings are used at least on the substrates because of their transparency which makes optical visibility possible. The two substrates are kept at the desired spacing by means of spacing members and are connected together in an airtight manner at the periphery. Inside there is a gas atmosphere. When applying a voltage to opposite electrodes a blue glow discharge, used for indication, occurs at the cathode. The cathode electrodes on one substrate are arranged as necessary to enable numerical, alpha numeric, cross or point raster representation are possible using them. In order to be able to apply the required voltages to the electrodes, airtight ducts are necessary. These ducts have already been proposed in great numbers. Ducts are even known in the form of electrically conductive coatings.